The present invention pertains to a brake power booster for motor vehicles with a brake power booster housing, at least one vacuum chamber and at least one additional pressure chamber, into which ambient pressure can be admitted during the actuation of an actuating pedal for the brake system of the motor vehicle, which actuating pedal is connected to the brake power booster, and into which the vacuum can be established in the non-operative position of the actuating pedal. The vacuum chamber and the pressure chamber are separated from one another by a displaceable piston. Furthermore, the brake power booster has at least one additional vacuum chamber, which can be connected to the pressure chamber via a switching device.
To assist the driver of the motor vehicle in the case of a braking operation and to provide additional braking power for actuating the brake system, brake power boosters of this type are now customarily used in the automobile industry. To boost the brake power, the assistance of the vacuum generated by the engine is utilized, and the brake power introduced into the brake system by the pivoting of the actuating pedal can be boosted up to fivefold. This is achieved, in principle, by the vacuum generated by the engine being admitted into both the vacuum chamber and the pressure chamber of the brake power booster in the non-operative state of the brake system so that they are at equilibrium. A pivoting of the actuating pedal of the brake system interrupts the connection present between the two chambers and opens the rear pressure chamber of the brake power booster, which faces the actuating pedal, to the atmospheric air, so that air under atmospheric pressure can flow into this pressure chamber. The piston located between the vacuum chamber and pressure chamber is displaced by the atmospheric pressure, together with the diaphragm connected thereto, in the forward direction, i.e., in the direction of the engine and the pivoting movement of the actuating pedal is thus assisted, and the movement of the piston acts on the piston rod of a connected main brake cylinder via suitable transmission members. After the end of the pivoting of the actuating pedal, the interrupted connection between the pressure chamber, the vacuum chamber and the engine-side vacuum connection is again established, so that a rearward movement of the actuating pedal into its starting position is made possible.
It is problematic for the use of this prior-art brake power booster that the necessary vacuum can no longer be provided to the sufficient extent by the modem gasoline and diesel engines being increasingly used. This applies especially to engines with fuel injection, in which the vacuum generated by the engine is no longer sufficient to bring about the desired additional boosting of the brake power and the necessary braking dynamics. This problem is remedied by the use of additional vacuum pumps, but they are disadvantageous because they require space for their installation and, in addition, also cause a rather substantial increase in the manufacturing costs of the entire brake system.
Increasing the area of the piston of the brake power boosters used is also ruled out as a possible solution because of the limited space conditions in the engine compartments of modern motor vehicles.
The object of the present invention is therefore to further improve a brake power booster for the brake system of a motor vehicle such that a sufficient amount of vacuum is always present for a sufficient number of successive braking operations with a simple design. The costs for such a brake power booster shall increase only slightly, if at all, compared with the brake power booster variants used hitherto.
A brake power booster with a brake power booster housing has at least one vacuum chamber and at least an additional pressure chamber, into which ambient pressure can be admitted during the actuation of an actuating pedal for the brake system of the motor vehicle. The actuating pedal is connected to the brake power booster. A vacuum can be established in the pressure chamber in the non-operative position of the actuating pedal, wherein the vacuum chamber and the pressure chamber are separated from one another by a displaceable piston. The brake power booster has at least one additional vacuum chamber, which can be connected to the pressure chamber via a switching device.
According to this technical teaching, it is advantageous for the switching device to establish the connection between the pressure chamber and the additional vacuum chamber after the return of the actuating pedal after the actuation process.
The additional vacuum chamber forms an energy reservoir here, which can be used during the braking operation and is charged from the engine during time periods during which no braking operation takes place. The storage of the vacuum guarantees that the low vacuum still provided will be sufficient for a sufficient number of braking operations even in the case of the modern motor vehicle engines currently in use. The additional vacuum reservoir ensures that the vacuum necessary during the return of the piston of the brake power booster is also sufficient for a rapid succession of braking maneuvers despite the weak suction effect of the engine. The special design according to the present invention does not require an additional foreign energy source but only additional costs due to the provision of a suitable switching device, with which the additional vacuum chamber can be connected to the pressure chamber.
It proved to be particularly advantageous for the additional vacuum chamber of the brake power booster housing to be arranged in a stiffening cavity. Stiffening cavities made in plastic within the brake power booster housing are common and present in all customary designs of brake power boosters because of the necessary strength of the brake power booster housing. These cavities can be utilized in the manner according to the present invention without enlarging the overall installation volume of the brake power booster for the necessary additional vacuum chamber. Thus, there are no additional costs due to an external vacuum reservoir connected to the brake power booster.
According to another embodiment of the present invention, provisions are made for the switching device to be designed as a solenoid on-off valve.
An exemplary embodiment of the subject of the present invention will be explained in greater detail below on the basis of the drawing attached.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.